Electrochemical cell devices are typically made up of a plurality of electrochemical cells, arranged in groups or stacks, and commonly serve to: electrolytically disassociate water or another liquid (with or without dissolved constituents) into its components (i.e., electrolysis cells), or catalytically combine hydrogen or other fuel and an oxidizer (i.e., fuel cells), with electricity being either supplied or generated, respectively. Other related functions for electrochemical cell devices include their use as compressors, separation and/or purification means, sensors, and combinations of these functions.
Within arranged groups or stacks, each electrochemical cell includes a cathode, an electrolyte (e.g., a membrane), and an anode. In Proton Exchange Membrane or PEM cells, where the electrolyte is a cation exchange membrane, the cathode/membrane/anode assembly (i.e., “membrane electrode assembly” or “MEA”) is typically supported on both sides by flow fields made up of screen packs or channeled plates. Flow fields, usually in the form of expanded metal or woven screens, or adhesive-bonded, laminated, or machined assemblies, facilitate fluid movement, removal of product water, and also serve to provide in, for example, PEM cells, mechanical support for the MEA.
By way of example, U.S. Pat. No. 5,316,644 to Titterington et al. teaches an electrochemical cell electrode plate structure that comprises a laminar assembly of at least two substantially identically configured and etched plate-shaped components. The plate-shaped components are adhered or bonded together using so-called laminating substances such as various epoxy resins, silicon and FLUOREL® elastomers and TEFLON® fluoroethylene propylene or FEP copolymers (see col. 9, lines 11 to 16, of U.S. Pat. No. 5,316,644). Cells made using these laminated electrode plate structures are known to have a high degree of flatness and strength. The process used to build these plate structures, however, is both time consuming and difficult to control. Moreover, plate structures that are built using this process are comprised of distinct layers that may degrade or exhibit high resistance at the interfaces.
A need exists for an electrochemical cell that overcomes the drawbacks associated with cells made using adhesive-bonded or laminated plate structures.
The present invention satisfies this need by providing an electrochemical cell that comprises two or more diffusion bonded layers, the diffusion bonded layers demonstrating excellent conductivity and improved resistance to delamination.
In a preferred embodiment, the inventive electrochemical cell comprises a diffusion bonded laminar or thin plate assembly in the form of, for example, a partially or fully diffusion bonded bipolar plate assembly.
The present invention further provides an arranged group or stack of the above-described electrochemical cells, with each such electrochemical cell preferably comprising either a partially or fully diffusion bonded bipolar plate assembly.
Each electrochemical cell in the stack will typically employ a porous plate/frame assembly for water/gas separation. Such an assembly may utilize a metallic or polymeric porous membrane. For metallic porous membranes (e.g., sintered metallic porous membranes), the membrane may be directly diffusion bonded into a bipolar plate assembly. For polymeric porous membranes, the membrane is preferably incorporated into the cell as a separate item. For example, the polymeric porous membrane would be supported by a first diffusion bonded plate assembly (e.g., oxygen screen/frame assembly) on one side, and a second diffusion bonded plate assembly (e.g., water chamber//divider sheet//coolant chamber//divider sheet//hydrogen chamber) on the other side.
In a first more preferred embodiment, the electrochemical cell stack of the present invention has internal manifolds positioned within the active area of each electrochemical cell, with each cell comprising an MEA and a partially or fully diffusion bonded bipolar plate assembly. The electrochemical cell stack in this embodiment is preferably a passive water removal cell stack employing hydrophilic porous plate/frame assemblies for water/gas separation, which is suitable for zero gravity operation.
In a second more preferred embodiment, the electrochemical cell stack has external manifolds (i.e., manifolds positioned outside the active area of each cell), which communicate with the active area of each electrochemical cell, with each cell comprising an MEA and a partially or fully diffusion bonded bipolar plate assembly.
Also provided by way of the present invention is a method for passive water removal from an electrochemical cell or cell stack, the method comprising:
providing one electrochemical cell or an arranged group or stack of cells, as described above, wherein each cell includes an MEA having an anode side and an opposing cathode side, open structures (e.g., screen/frame assemblies) located on opposing sides of the MEA, a hydrophilic porous plate or porous plate/frame assembly adjacent to and in intimate contact with the open structure located on the cathode side of the MEA, and a water collection chamber located on an opposing side of the hydrophilic porous plate or porous plate/frame assembly; and
maintaining the open structure located on the cathode side of the MEA at a pressure greater than the pressure in the water collection chamber in the cell(s) during operation of the electrochemical cell or cell stack.
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.